1. Field of the Invention
This invention relates to pinch roller drive mechanisms.
2. Background Art
Roller coaster rides require a means of propelling or driving the passenger cars to an elevated region of the ride, so that thereafter the cars can coast under the force of gravity. One well known prior art drive scheme uses a chain drive that pulls the passenger cars to the top of an incline. The chain is a linked loop that traces a path, for example, between two rails on which the passenger cars ride. The cars latch onto the chain and travel with the chain as it moves from the bottom of an incline to the top of the incline. At or about the apex of the incline, the cars are unlatched from the chain, the chain is looped below the track back to the bottom, and the cars begin a descent from the apex, powered by gravity.
A disadvantage of prior art chain drive systems is the requirement that the coaster must travel in a straight line. The chain forms a vertical loop, much as a chain on a bicycle, circles a drive gear and other tensioning rollers, usually at the top and bottom of the incline. It has heretofore not been practical to provide a chain drive that can be configured, for example, in an inclined spiral. It is desirable to provide a drive mechanism that permits a coaster to be driven upward in a spiral path, thus providing the ability of added entertainment for the coaster's passengers.
One chain drive scheme for propelling rail type amusement cars is described in Schwarzkopf, U.S. Pat. No. 4,361,094.
Another prior art drive system utilizes pinch wheel drives. In a pinch wheel drive system, the car to be driven includes a surface, often referred to as a "fin" mounted to the lower surface of the car. The fin is contacted on both of its sides by drive rollers. The rollers are rotating in opposite directions so as to propel the fin, and ultimately, the car, in one direction. The fin passes through a pinch roller "gap" between the pinch rollers. Typically the distance between the rollers to define the gap is fixed by positioning the rollers at a desired location and fixedly mounting them to a frame.
The rollers engage the fin with a large amount of force, so as to be able to impart driving force to the fin. This forced engagement, or "pinching" of the rollers must be consistent and approximately equal so that both wheels provide force to the fin. The pinching force is generally provided by a spring force that "squeezes" the pinch rollers together. Often the pinch rollers engage each other in the absence of a drive fin. Because the wheels are somewhat elastic or deformable, a gap can be created when a drive fin enters the pinch wheels.
A disadvantage of pinch drives of the prior art is the fact that motion of the coaster is restricted to a straight line. When the fin is at an angle to the wheels, it is difficult to provide adequate longitudinal force to both sides of the fin. The result is an inability to consistently drive the coaster. This problem is caused in part by the "chording" effect of a drive fin as it travels through a curve. The fin is physically displaced towards the inside of the curved path during travel. This creates a force against one of the pinch wheels. When the pinch wheels are fixedly mounted, as in the prior art, unwanted forces are generated on both the pinch wheels and the fin, resulting in possible failure. In other cases, the chording effect can cause displacement of the pinch wheel, pulling the drive fin away from the other pinch wheel and resulting in a lack of driving force and misregistration of the pinch wheels.
Another disadvantage of prior art pinch drives systems is the fact that a large spring force is required to provide the pinching force to the pinch wheels. This spring force causes the pinch wheels to wear against each other whenever they are not pinching against a drive fin. Over time, the frictional force acting on the wheels wears them down, causing the gap to widen, reducing performance and causing slipping of the fin. This creates a need for constant maintenance and adjustment of the position of the pinch wheels and of the urgent force applied to them.
A prior art pinch roller drive is described in German patent DD 252,267 A1. The system uses drive rollers mounted on a "U" shaped assembly that includes a scissoring mechanism. The scissors mechanism is activated so that the pinch wheels engage a rail beneath a car to be driven.
Brachand, French patent 2,595,310 describes a pinch wheel transport scheme that uses rotating wheels set in a guide track. The scheme uses a fixed gap between the rollers. The description includes an illustration of curved motion but does not illustrate self tensioning or self aligning drive wheels.
Nakagawa, Japanese patent 40-3-239661 describes a pinch roller driven dolly that includes a braking means that is automatically activated to prevent gaps between dollys that are pushed by the drive dolly.
Japanese patent 40-3-104,463 to Nakagawa describes a pinch drive system. Pinch rollers are brought into contact with upper and lower sides of a fin of a body to be driven. A scissors mechanism applies pinching force to the pinch wheels so that they contact the fin.
Soviet Union patent SU 1609-729-A describes a pinch drive system that includes tightening elements to press the drive wheels to the fin at a set force.
Schwarzkopf, U.S. Pat. No. 3,403,633 is directed to an amusement ride that uses pinch rollers to propel the car by engaging a drive plate member on the car. The roller pairs use resilient pneumatic tires that bear against the faces of a generally flat plate affixed to the car to be driven. The plates are described as being curved to conform to the radius of curvature of the track. The rollers are of a fixed gap type and susceptible to excessive wear.
U.S. Pat. No. 4,003,329 to Robinson is directed to a combination positioning and propelling apparatus for barges. Wheels are disposed on opposite sides of a barge to index and position the barge. In Robinson, the wheels are driven to impart a motive force to the barge. The wheels may be positioned at various widths to accommodate various size barges.
Schwarzkopf, U.S. Pat. No. 4,361,094 describes a drive system for roller coasters that utilizes a pair of chains having a series of links and segments. The system is to enable the use of pinch wheel drivers in both curved and straight sections of track. The drive member, or fin, of the '094 scheme is made limitedly laterally flexible so that it can conform to and align with the drive rollers in the curved and straight track sections.
U.S. Pat. No. 4,520,732 to Schwarzkopf is directed to a suspended roller coaster where the cars are suspended from an overhead rail. The '732 patent does not describe a drive mechanism for the coaster.
Sticht, U.S. Pat. No. 4,619,205 is directed to a conveyer arrangement for moving a carrier in a desired direction. A drive associated with one side of the carrier engages the one side and propelling the carrier in the drive direction. A conveyer roller presses guide rollers against the side of the carrier.
An apparatus for conveying a travelable body is described in Kiuchi, U.S. Pat. No. 5,067,413. Pivotally mounted drive rollers are brought into contact with a drive member and the drive rollers are rotated to propel the vehicle.